1. Field of the Invention
The present invention relates to a method of manufacturing a thin film magnetic head, and more particularly to a method of manufacturing a combination type thin film magnetic head constructed by stacking an inductive type writing thin film magnetic head and a magnetoresistive type reading thin film magnetic head on a surface of a substrate in an electrically insulating and magnetically isolated manner.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. A combination type thin film magnetic head is constructed by stacking an inductive type thin film magnetic head intended for writing and a magnetoresistive type thin film magnetic head intended for reading on a substrate, and has been practically used. In general, as a reading magnetoresistive element, an element utilizing anisotropic magnetoresistive (AMR) effect has been used so far, but there has been further developed a GMR reproducing element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than that of the normal anisotropic magnetoresistive effect by several times.
In the present specification, elements exhibiting a magnetoresistive effect such as AMR and GMR reproducing elements are termed as a magnetoresistive reproducing element or MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits/inch.sup.2 has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes.
A height of a magnetoresistive reproducing element (MR Height: MRH) is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. The MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH can be obtained by controlling an amount of polishing the air bearing surface.
At the same time, the performance of the recording magnetic head is also required to be improved in accordance with the improvement of the performance of the reproducing magnetic head. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a write gap at the air bearing surface has to be reduced to a value within a range from several micron meters to several sub-micron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head.
One of factors determining the performance of the inductive type writing thin film magnetic head is a throat height TH. This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. The reduction of this throat height is also decided by an amount of polishing the air bearing surface.
FIGS. 1-12 show successive steps of a method of manufacturing a conventional standard thin film magnetic head and a completed thin film magnetic head. It should be noted that the thin film magnetic head is of a combination type in which the inductive type thin film magnetic head for writing is stacked on the reproducing MR element.
First of all, as shown in FIG. 1, an alumina insulating layer 112 is deposited on a substance 111 made of, for instance AlTiC and having a thickness of about 5-10 .mu.m.
Next, as shown in FIG. 2, a bottom shield magnetic layer 113 which protects the MR reproduction element of the reproducing head from the influence of an external magnetic field, is formed with a thickness of 3 .mu.m. Then, as shown in FIG. 3, an insulating layer 114 of thickness 100-150 nm serving as a shield gap layer is formed by sputtering alumina. Furthermore, as illustrated in FIG. 3, a magnetoresistive layer 115 made of a material having the magnetoresistive effect and constituting the MR reproduction element is formed on the shield gap layer 114 with a thickness of several tens nano meters and is then shaped into a given pattern by the highly precise mask alignment.
Then, as shown in the FIG. 4, an alumina insulating layer 116 similar to the alumina insulating layer 114 is formed such that the magnetoresistive layer 115 is embedded within the insulating layers 114 and 116.
Next, as shown in the FIG. 5, a magnetic layer 117 made of a permalloy is formed with a thickness of 3-4 .mu.m. This magnetic layer 117 has not only the function of the upper shield layer which magnetically shields the MR reproduction element together with the above described bottom shield layer 113, but also has the function of one of poles of the writing thin film magnetic head. Here, the magnetic layer 117 is called a first magnetic layer by taking into account the latter function.
Then, as depicted in FIG. 6, a write gap layer 118 made of a nonmagnetic material such as alumina and having a thickness of about 150-300 nm is formed on the first magnetic layer 117, and an electrically insulating layer 119 made of a photoresist is formed on the gap layer into a given pattern by the mask alignment of high precision. Further, a first layer thin film coil 120 made of, for instance a copper is formed on the photoresist layer 119.
Continuously, as shown in FIG. 7, after forming an electrically insulating photoresist layer 121 on the thin film coil 120 by the highly precise mask alignment, the photoresist layer is sintered at a temperature of, for example 250.degree. C.
In addition, as shown in FIG. 8, a second layer thin film coil 122 is formed on the flattened surface of the photoresist layer 121. Next, after forming a photoresist layer 123 on the second layer thin film coil 122 with the highly precise mask alignment, the photoresist layer is flattened by performing the sintering process at a temperature of, for example 250.degree. C.
As described above, the reason why the photoresist layers 119, 121 and 123 are formed by the highly precise mask alignment process, is that the throat height TH and MR height MRH are defined with reference to a position of the edges of the photoresist layers.
Next, as shown in FIG. 9, a second magnetic layer 124 made of, for example a permalloy and having a thickness of 3-4 .mu.m is selectively formed on the gap layer and photoresist layers 119, 121 and 123 in accordance with a desired pattern.
This second magnetic layer 124 is coupled with the first magnetic layer 117 at a rear position remote from the magnetoresistive layer 115, and the thin film coil 120, 122 passes through a closed magnetic circuit composed of the first and second magnetic layers. The second magnetic layer 122 includes a pole portion having desired size and shape for defining a track width W.
Furthermore, an overcoat layer 17 made of alumina is deposited on the exposed surface of the gap layer 118 and second magnetic layer 124. In an actual thin film magnetic head, electric conductors and contact pads for performing the electrical connection to the thin film coils 120, 122 and MR reproduction element are formed, but they are not shown in the drawings.
In an actual manufacturing process, the above mentioned substrate 111 is formed by a wafer, and after forming a number of thin film magnetic head units in the wafer in matrix, the wafer is divided into a plurality of bars, in each of which a plurality of thin film magnetic head units are aligned, and finally the bar is divided into respective thin film magnetic heads.
That is to say, as shown in FIG. 10, a side surface 126 of the substrate 111 on which the magnetoresistive layer 115 is exposed is polished to form an air bearing surface 127 which is opposed to a magnetic record medium. During the formation of the air bearing surface 127, the magnetoresistive layer 115 is also polished to form a MR reproducing element 128, and at the same time the throat height TH and MR height MRH are determined.
When the air bearing surface is polished, it is difficult to perform the polishing while the throat height and MR height are actually monitored. Therefore, a resistance measuring circuit is connected to the conductive patters (not shown) connected to the magnetoresistive layer 115, a change in resistance which is reduced in accordance with a reduction of the height of the magnetoresistive layer due to the polishing is measured as a change in a current, and an amount of polishing is calculated from the variation in the thus measured current. That is to say, by performing the polishing operation until the resistance value of the MR reproducing element 128 becomes a predetermined value, desired throat height and MR height are attained.
FIGS. 10, 11 and 12 cross sectional, front and plan views, respectively showing the completed conventional thin film magnetic head, while the overcoat layer 125 is omitted. It should be noted that in FIG. 10, the alumina insulating layers 114 and 116 surrounding the MR reproducing element 128 are shown as a single insulating layer, and in FIG. 12, the thin film coil 120, 122 is shown concentrically for the sake of simplicity.
As clearly shown in FIG. 10, an angle .theta. (apex angle) between a line S connecting side edges of the photoresist layers 119, 121, 123 for isolating the thin film coil 120, 122 and the upper surface of the second magnetic layer 124 is an important factor for determining the performance of the thin film magnetic head together with the above described throat height TH and MR height MRH.
Furthermore, as shown in the plan view of FIG. 12, the width W of a pole portion 124a of the second magnetic layer 124 is small. Since the width of the track recorded on the magnetic record medium is defined by this width W, it is necessary to narrow this width as small as possible in order to achieve a high surface recording density.
In order to improve the surface recording density on the magnetic record medium, it is required to improve the performance of the recording head and reproducing head. In the above explained method of manufacturing the thin film magnetic head, a control in the order of sub-microns utilizing the semiconductor manufacturing technique is indispensable. The throat height and apex angle of the inductive type writing thin film magnetic head and the MR height of the reading thin film magnetic head including the MR reproducing element have a large influence upon the manufacturing yield of the combination type thin film magnetic head.
As explained above with reference to FIGS. 1-12, in the known method of manufacturing a thin film magnetic head, the MR height is determined by controlling an amount of polishing such that the measured resistance value of the magnetoresistive layer 115 of the MR reproducing element becomes a desired value. However, it is difficult to obtain the desired MR height by such a method, because there is not a definite or constant relationship between the resistance value of the magnetoresistive layer 115 and the MR height. That is to say, the resistance value of the magnetoresistive layer 115 fluctuates in accordance with its composition and manufacturing condition, and thus even if the resistance becomes a predetermined value, the MR height might not be a given value. Therefore, in the known method, although the MR reproducing element has a desired resistance value, the MR height might deviate from a desired value and the performance of the combination type thin film magnetic head might be decreased.
Moreover, even if the MR height becomes a desired value by polishing the air bearing surface by monitoring the resistance of the magnetoresistive layer 115, the throat height and apex angle of the writing thin film magnetic head could not always be identical with desired values. That is to say, upon manufacturing the writing thin film magnetic head, the reference position of throat height zero is defined by the edge of the insulating layer 119 and the apex angle is defined by the profile of the insulating layers 119, 121, 123, but these insulating layers are deformed by the heating treatment at about 250.degree. C. during the formation of the thin film coil 120, 122, and the throat height zero position and the profile of the insulating layers might be changed. Particularly, when the photoresist insulating layers 119, 121, 123 have a large thickness, the deviation of the pattern might be large such as about 0.5 .mu.m. Then, the fine throat height from several microns to sub-microns could not be realized in a reproductive manner and a desired apex angle could not be obtained. Further, when the thick insulating layers are used, the deviation of pattern might be increased due to unevenness of the film thickness.
For instance, in the high frequency thin film magnetic head, the throat height not larger than 1.0 .mu.m is required, but due to the above explained large error up to 0.5 .mu.m, the throat height might deviate from the desired value, and the manufacturing cost might be increased. Moreover, since an allowance for the apex angle is very small, the deviation in the apex angle due to the deformation of the profile of the insulating layers might exceed the allowance.
In order to mitigate the above mentioned drawbacks, in Japanese Patent Application Laid-open Publication Kokai Sho 63-29315 and corresponding U.S. Pat. No. 4,689,877, there is proposed a method, in which a plurality of switch contacts which are successively opened in accordance with the progress of polishing and guide resistors whose value is continuously changed in accordance with the progress of polishing are formed on both end portions of a bar in which a plurality of thin film magnetic head units are aligned, and the polishing is controlled by monitoring the opening of the switch contacts and resistance value such that the throat height becomes a desired value.
However, in this known method, additional manufacturing steps are required for forming the switch contacts and guide resistors at both ends of the bar, and thus a through-put is decreased to a large extent. That is to say, a step of forming the switch contacts from a conductive material and a step of forming the guide resistors from a resistive material are additionally or separately required. Moreover, since the plural switch contacts are formed such that distances between successive switch contacts are much longer than dimensions of electrode elements of the switch contacts viewed in the polishing direction, a fine control such as 0.1-0.5 .mu.m could not be performed accurately even if the polishing is controlled by a combination of a stepwise change of the throat height measured by the opening or cut-off of the switch contacts and a continuous change of the throat height measured by the continuous resistance change of the guide resistance.
Furthermore, in case of controlling a polishing amount for the air bearing surface, the reference position of throat height zero should not be shifted largely. However, in the known method, since the insulating layers 119, 121, 123 are deformed largely due to the heating treatment as stated above, the throat height could not be controlled accurately. Further, in the known method, a deviation of the apex angle from a desired value could not be compensated for at all.
In order to improve the surface recording density on the record medium, it is also required to increase a sensitivity of the reading thin film magnetic head including the reproducing MR element. To this end, it is advantageous to utilize the GMR layer having a higher sensitivity. However, characteristics of the GMR layer are largely affected by heating. For instance, after forming the reproducing element having the GMR layer, when the insulating layers are heated, the characteristics of the GMR layer might be degraded extremely. The heating process is indispensable for flattening the thin film coil and improve the electrical isolation between coil windings.